In U.S. Pat. No. 4,850,230 issued to L. B. Eldridge, there is illustrated a measuring system for determining the pull force placed on a pull tab during the formation of the opening in a can, which patent is incorporated herein by reference thereto. The Eldridge patent uses a load cell which generates signals representing the forces applied thereto during the opening operation and sends such signals to a computer and recording apparatus. In order to verify the accuracy of the measurements, it is necessary to calibrate the load cell at periodic intervals.
One method for calibrating the load cell involves the use of a mechanical, spring-type, dial pressure gage to place known forces on the load cell. The load cell transmits a signal, such as a voltage, for each known force to a computer-recorder, which establishes a load slope between a no force condition and a maximum force applied condition. Known forces between a no force condition and a maximum force condition may also be used to establish a load slope. After being programmed, the computer-recorder will respond to all signals received from the load cell and record any force applied thereto between the no force applied condition and the maximum force applied condition. While this system does calibrate the load cell, it takes considerable time to perform. Therefore, it was desirable to develop calibration apparatus which would be an automatic function of the measuring apparatus described in the Eldridge patent.